@article{melo_souza_bastos_cardoso_2020,  title={Critical levels and sufficiency ranges for leaf nutrient diagnosis in cowpea grown in the Northeast region of Brazil},  volume={51},  ISSN={1806-6690},  url={https://doi.org/10.5935/1806-6690.20200071},  DOI={10.5935/1806-6690.20200071},  number={4},  journal={Revista Ciência Agronômica},  publisher={Universidade Federal do Ceará},  author={Melo, Francisco de Brito and Souza, Henrique Antunes de and Bastos, Edson Alves and Cardoso, Milton Jose},  year={2020},  pages={e20196954} }